Infrared control device



0. T. FRANCIS INFRA-RED CONTROL DEVICE June 27, 1944.

Filed June 29, 1939 Patented June 27, 1944 UNITED STATES PATENT OFFICE2,352,377 INFRARED CONTROL DEVICE Oliver T. Francis, Renville, Minn.

' Application June 29, 1939, Serial No. 281,964

I 14 Claims. This invention relates to light control devices,

and more particularly to signal control by the longer infra-redradiations, or heat waves.

Various means of infra-red light control devices have been used. Thesemeans may be summarized as follows:

1. Devices using the thermocouple, or bolometer. While such devices areresponsive to small changes in temperature, the heat capacity of suchdevices is usually of the order of several hundred ergs per degree.Consequently the response to weak sources of radiant energy is veryslow, of the order of several seconds or more.

2. Photo-electric cell devices. While the dynamic response of some ofthese devices is excellent, and their sensitivity satisfactory, they arenot responsive to radiations longer than 1.2 mu. While radiations ofthese wavelengths penetrate haze, they have little advantage overwavelengths in the visible spectrum in penetrating fog. A transmittingsource must be of the order of 2000 degrees absolute before giving offappreciable amounts of energy of such short wave lengths, therefore suchdevices are useless in recording the presence of heat radiating objectssuch as airplanes, automobiles, and the human" body. 7

3. Devices which utilize varying vapor pressures of gases in thepresence of the liquefied gas.

One type of such apparatus is the common furnace temperature control,utilizing mercury the liquified gas and measuring the vapor pressure bya gage of the well known ionization gage type. vSuch devices can neverbe made responsive to changes in extremely small energy sources,

usually charcoal, combined with the thermal ex pension of the gas. Knowndevices of this type comprise means for transforming modulated waves ofradiant energy into compressional waves, to move a diaphragm, andtransforming the movements of said diaphragm into electrical vibrations,which are further amplified by vacuum tube amplifiers. Such devices,using oxygen as the adsorbent gas are responsive to the fog penetratingradiations between 5 and 15 mu. The heat of evaporization of oxygen is.08 electron volts or 15 mu per molecule, and the attraction of thecharcoal for the oxygen is small and does not add much'to this value.Published reports indicate that such devices are capable of picking upheat given off by an airplane, automobile steam boiler, etc., atdistances of several miles. While such reports would seem to indicatesens tivity of such devices, further consideration shows that such isnot the case. The energy given off by an airplane motor is often of theorder of 1000 kilowatts. While the greater portion of this energy may bedissipated in convection current a considerable portion is radiated. Theradiant energy received at a distance of twenty milesvmay be overseveral ergs per second per square foot; Radio receivers, andphoto-electric cellsare both responsive to less than a billionth of thatamount of energy. The insensitivity of existing heat recording devicesis therefore apparent. This lack of sensitivity is one of the causes ofthe very poor dynamic response at. frequencies greater than one cycledue to the thermal capacity of the liquified gas and the fact thatcondensation of the gas on the various portions of the apparatusconstitutes a further thermal load. The heat .of evaporization of amolecule of mercury is given by Eldridge per second, and limits theusefulness of the devices to burglar alarm systems, and similarpurposes. Other causes of the poor dynamic re- "sponse of th s type ofdevice is the relatively I large amount of energy required for themovein Physical Basis of Things, 1934 edition, page 1 83, as 57 atomicergs. Since 96 atomic ergs equals one electrol volt, as he states onpage 331, the heat of vaporization of the mercury molecule equalsapproximately .6 electron volts of energy.

brought out by Zworykin and, Wilson in Photo cells and theirApplication, 1932 edit on, page 321, next to last formula on page .6electron volt is approximately the amount of energy contained in aphoton of 2 mu wavelength, and such wavelengths do not appear inappreciable magnitude until the transmitting source attains atemperature well over 1000 degrees absolute.

4. Devices which utilize varying vapor pressures of gas in the presenceof an adsorl'ient,

ment of the diaphragm, the thermal capacity of the adsorbent, the factthat the condensation of the oxygen on the adsorbent is slowed up byallowing the inert gases present such as nitrogen, and the rare gases toform a shield aroundthe adsorbent, until the oxygen difiuses' through tothe adsorbent.

It is an object of this invention to provide a radiant energy signallingdevice which shall be sensitive to the fog penetrating radiationsbetween 5 and 15 mu and longer wavelengths, .in which the dynamicresponse shall be rapid, which shall be rugged in construction, and easyto operate, and wherein the difliculties mentioned above shall not bepresent.

Another object is to provide a device which shall be responsive to anydesired heat wavelength.

Another object is to provide means for receiving quanta of low energy,and means for producing light quanta of higher energy corresponding innumber to the low energy light quanta received, by evaporation ofmolecules of a gas with said low energy quanta, and releasing said highenergy quanta by combustion of said molecules.

It has long been known that the vapor pressure of a gas'existing over anadsorbent, varies as the temperature of the adsorbent. Charcoal at roomtemperature will adsorb 90 times its volume of ammonia gas, 35 times itsvolume of carbon dioxide, 19 times its volume of chlorine, 1.7 t mes itsvolume of hydrogen. As the temperature of the charcoal decreases thevolume of the gas adsorbed increases until at minus 185 degreescentigrade, it will adsorb 135 times its volume of hydrogen. It is anobject of this invention to vary the vapor pressure of a gas overcharcoal in accordance with variations in radiant energy received, andto provide novel means for indicating said pressure variations.

Another object is to release molecules of gas from an adsorbent by lowenergy photons, to cause said molecules to produce high energy photonsby chemically combining with molecules of another substance, and toprovide photo-electric means for indicating the presence of said highenergy photons.

It is well known that the charcoal in a gas mask will adsorbsubstantially all of the gas such as chlorine from a moving stream ofair passing through it in an extremely short periodof time, whereas ifthe charcoal were exposed to the air the time required for diffusion ofthe chlorine through the air would prevent rapid adsorption of thechlorine. The moving stream of air in the gas mask brings the chlorineinto intimate contact with the charcoal particles, thereby permittingsubstantially instantaneous removal. It is an object of this inventionto use a moving stream of gas over an adsorbent to circumvent the timedelays required by diffusion in existing apparatus, and to furtherincrease the dynamic response by the cooling eflect of said stream onsaid adsorbent, by preventing build up of gas pressures. This coolingeffect does not lessen the response of the device to radiant energyreceived dueto the fact that it operates by the phenomenon of diffusion,to prevent build up of vapor pressures, which vapor pressures wouldpromote condensation with resultant heating.

It is well known that the catalyst spongy platinum becomes incandescentwhen exposed to the gas of wood alcohol and the gas oxygen of the air.It is an object of this invention to vary the magnitude of one of saidgases applied to said platinum, in accordance with a received signal,thereby varying the temperature of the surface of the platinum and toprovide means for recording slight variations in said temperature.

Another object is to provide a novel light transmitting source whichshall be rich in the longer heat waves, and capable of rapid dynamicresponse.

With these and other objects in view the invention will be more readilyunderstood by reference to the figures taken in connection with thefollow ng description, wherein, the figure illustrates a light controldevice capable of penetrating fog.

Referring to the figure, light transmitting station I is composed of ahigh vacuum tube 2, containing an anode 3, a cathode 4, and a controlelectrode 5. Anode 3 comprises a tungsten target of small dimensions, ofthe order of an eighth of an inch in diameter and is supported by a leadwire entering the evacuated enclosure 2 in the upper part of the bulb.The anode 3 is located at the focal point of a parabolic reflector 58,and is furnished current from the secondary of transformer 6, theprimary of which is supplied with current from an alternating currentsource I. The cathode 4 is heated by an A battery 8. Electrode 5|,capable of dissipating considerable heat, has been placed near the anodeand connected to the cathode. A disc 55 with a hole 56 has been providedto concentrate the electron beam to anode 3. C battery 9 impresses ahigh negative potential on control electrode 5, through resistance Ill.When key H is closed this negative potential is removed and the platecurrent is allowed to flow from anode 3 to cathode 4. The portion ofvacuum tube 2 nearest the reflector 5!! is closed by a window I2 such asrock salt, florite, or sylvine, all of which substances are transparentto the far infra-red radiations. Since it is difficult to maintain highvacuum with seals of this type a vacuum pump l3 of conventional type isconnected to tube 2 for use when necessary.

The receiving station I4, is composed of an infra-red sensitive devicel5, containing an adsorbent such as charcoal l6, which is located at thefocal point of parabolic reflector IT. The side of the device l5 nearestthe reflector i1 is closed by a window l8 transparent to the farinfra-red radiations. Since the device I5 is above atmospheric pressureno special precautions need to be taken with the seal of the window. Thedevice I5 is supplied w th a stream of gas from a large container l9through a very small tube 20 and valve 52. This gas may be replenishedfrom time to time through valve 38 and tube 31 The kind of gas used incontainer l9 depends upon the frequency of radiations to which it sdesired to have the receiving station 14 respond, and the at mospherictemperature in which the device is operated. For the far infra-redradiations it s necessary to use a gas of low boiling point, since theenergy required to evaporize a molecule of gas from the adsorbent interms of electron volts is the sum of the energy requiredto evaporizethe molecule plus the energy of attraction of the adsorbent. For thedevice to respond to 15 mu a mixture of oxygen and helium issatisfactory, oxygen being the adsorbed gas, the helium not beingappreciably affected by the adsorbent at room temperatures. While it ispossible to use oxygen alone, I prefer to use it in combination with aninert gas in order that the stream of inert gas may tend to maintain theadsorbent at a constant temperature in accordance with the principles ofdiffusion previously described as the adsorbed gas is condensed andevaporized from the adsorbent. Furthermore the use of pure oxygen isaccompanied with an element of danger due to the possibility ofexplosion. Ordinary air may be used. For light quanta of energies higherthan 3 mu it is possible to use a gas such as a hydrocarbon, whosemolecular heat of evaporization is 4 or five mu. For extremely lowenergy light quanta it is necessary to use hydrogen, with lowtemperatures, the molecular heat of evaporization of hydrogen being mu.

The gas from the sensitive device I5 proceeds through tube 2| past valve22, where it joins gas from container 23 through tube 25 and valve 53.This latter gas may be wood alcohol, the liquid form of Which is shownat 24.

alcohol.

spongy platinum is to act as a catalyst to produce ignition of the woodalcohol vapors. It therefore Spongy platinum 26 is located in thepath ofthese gases as a catalyst, and glows due to the heat of combustion ofthe oxygen and the wood As indicated above the purpose of the maybe ofsmall dimensions or omitted entirely where vapor pressures of the oxygenand wood alcohol are of optimum value to maintain a flame without acatalyst. The use of an auxiliary igni-' tion means such as the spongyplatinum has the advantage of re-igniting the gases when the flame goesout. The refuse gases are discharged --'at opening 21.

' Surrounding the tube 2| is a photo-electric" cathode 28, on the outersurface of which-has been deposited a photo-active substance such as ath n layer of cesium oxide on the supporting -glass. Anode 29 furthersurrounds cathode 28 and both are inclosed in a highly evacuatedcontainer 36. Anode 29 is supplied with voltage from battery 3| througha high resistance 32. Vacuum tube amplifier with gridleak resistance 33amplifies the voltage across the high resistance 32 through condenser34. 'In the output circuit;-. of the amplifier 35 is' the primary oftransformer 51, the secondary of which in parallel with condenser 58forms a circuit tunedto the frequency of A. C. generator 1, the voltageacross which "is amplied' by'vacuum tube 66 in the output cir--' cuit ofwhich is connected an electro-responsive device in the form ofheadphones 36.

' In operation, when key H is closed high veflocity electrons fromcathode 4 heat anode 3 to incandescence at the frequency of A. C.genera-' tor Ii When' the cathode side of the secondary of transformer 6becomes positive, electrode 5| draws current from incandescent anode 3,thereby cooling it by electron evaporization, and reducing the thermaltime lag of the anode 3. The 7 high voltage electrons from cathode 4striking 3 produce secondary electrons, as is well known.

' The charge of 5| being negative at that instant the majority of themare forced back to anode 3, thereby producing infra-red photons. At thehigher frequencies of l the heating of anode 3 by electron bombardmentfrom cathode 4 and j the cooling by electron evaporizationbecomes a Isurface effect thereby largely doing away with the time lag due to thethermal capacity of the anode 3. The cooling effect of electron emissionis utilized in U. S. Patent No. 1,976,120, issued to me October 9,1934,to which reference is made.

The variations in radiations fromanode 3 are concentrated by reflectoron to a collector consis-ting of parabolic reflector H at the receivingstation I 4, where they are focused on to adsorbent l6, thereby varyingthe adsorption of the oxygen in the stream of gas passing from gascontainer I lflthrough tube 20. 'Since tube 2| is much larger 5 thantube 23 variations in pressure in sensitive device IE will produce largevariations ,in'the magnitude of thestr'eam of gas passing through thetube 2 I, and furthermore the oxygen content of the stream in the tube2! will increase as the magnitude of the stream increases by reason ofthe oxygen set free from the adsorbent. Gas from wood alcohol 24, whichmay be heated to give optimum vapor pressure, flows into conduit 2|.contact with spongy platinum 26 which is heated to the point ofincandescence. A flame also forms around it under such conditions as iswell known in experiments with spongy platinum as a catalyst. Photonsfrom the spongy plati- The combined gases in the tube 2| come in andcontrols electro-responsive device 36.

' at which point very slight changes in the oxygen content of the gasdue to variations in adsorption of adsorbent l6 in response tovariations of radiant energy received from light source 3, at thetransmitting station will produce appreciable response inelectro-responsive device 36.

- The adsorbent I6 is responsive to all radiations,

visible and infra-red up to 15 mu. In daylight operation when fogsbecome heavy it is desirable to screen out the diffused light energyfrom the fog, and this may be accomplished by color filter 54' in frontof the window to photo-responsive device l5 designated as 3.

One of the novel features of my invention constitutes a means forproducing variations in adsorption-of molecules of a gas in accordancewitlilow energy photons, impressed on an adsorbent, means for causingsaid molecules of said gas to chemically combine with molecules of someother substance, thereby producing photons of -higher energy, and meansresponsive to said higher energy photons.

-"While I have used the phenomenon of adsorption in illustrating myinvention, it is to be noted that some authors on physics make no"distinction between the phenomenon of adsorp- 1 tion and absorption,both involving the release of quanta of energy of low magnitude uponcondensation' of molecules, and where the word adsorption is used itwill include within its meaning absorption.

While, in light transmitting vacuum tube 2, I

Y have used a disc 55 as the means for focusing the electrons on theproper portion of the anode 3,

a it is evident that other means may be used, such electro-static andelectro-magnetic lenses.

While I have illustrated my device as a light {signalling system it isobvious that it could be used as a means of indicating the breaking ofthe beam by an object instead of by modulating the light source, such asin burglar alarm systems.

It is therefore evident that the invention may take widely differentforms from those illustrated without departing from its spirit. Theinvention is to be limited in scope only by prior art and as describedin the following claims. What is claimed is:

"l fThe method of indicating the presence of photons between 5 and 15mu, received from a variable source of radiant energy, which consists inevaporizing molecules of gas from an adfsorbent by said photons, inproducing higher en- '*'ergy photons than 5 mu by combustion of saidimolecules, in producing variations in an electric f current inaccordance with'the magnitude of said higher energy photons, and intranslating said var ations of electrical current into signals.

2. The method of indicating the presence of radiations between 5 and 15mu which consists in varying the vapor pressure of a gas in accordancewith variations in said radiations, in producing oxidation with saidgas, in producing an electrical current by the shorter than 5 muwavelength photons produced by said oxidation, and

in indicating the presence of said electrical current.

3. In a radiant energy control device, an adsorbent, a containercontaining gas capable of being adsorbed by said adsorbent, means forpassing a current of said gas over said adsorbent, means for varying theamount of said gas adsorbed by said adsorbent, said last meanscomprising means for focusing radiant energy on said adsorbent, andmeans for indicating the amount of said gas adsorbed by said adsorbent.

4. In a radiant energy control device, an adsorbent, a containercontaining a gas capable of being adsorbed by said adsorbent, means forpassing a current of said gas over said adsorbent, means for varying themagnitude of said gas current, said last means comprising means forfocusing radiant energy on said adsorbent, a substance, means forproducing a chemical reaction between said substance and said varyinggas current, and means for indicating the magnitude of chemical energyreleased by the combining of said substance and said varying current ofgas.

5. In a radiant energy control device, an adsorbent, a containercontaining gas for adsorption on said adsorbent, means for passing acurrent of said gas over said adsorbent, means for varying theadsorption of said current by said adsorbent, said last means comprisingmeans for focussing radiant energy on said adsorbent, a secondcontainer, containing a gas capable of chemically uniting with saidfirst gas, a catalyst for producing chemical reaction between said twogases, and means for indicating the temperature of said catalyst.

6. In a radiant energy control device, an adsorbent, a containercontaining a gas for adsorption on said adsorbent, means for passing acurrent of said gas over said adsorbent, means for producing variationsin said current, said last means comprising means for focusing radiantenergy on said adsorbent, a second container containing a second gascapable of uniting into chemical combination with said first gas, meansfor combining said second gas and said variable current of gas, acatalyst for producing said chemical combination, a photo-electricdevice, means-for impressing radiant energy from said chemicalcombination of said gases on said photoelectric cell, and means forindicating the magnitude of electrical current through said cell.

'7. In a radiant energy-control device, an adsorbent, molecules of a gasabsorbed on said absorbent, means for applying infra-red photons to saidadsorbent to evaporize the molecules of said gas from. said adsorbent, acolor filter for preventing visible radiations from reaching saidadsorbent, a. substance, means for causing chemical reaction betweensaid gas and said substance, and a photo-electric means for indicatingthe presence of visible photons produced by said reaction. I

8. In an infra-red device responsive to radiations longer than two mu,an adsorbent, means for passing a current of gas containing oxygen oversaid adsorbent, means for varying the magni-- tude of oxygen adsorbed bysaid adsorbent, said last means comprising means for focusing radiationson said adsorbent, a source of woodalcohol vapors, means for combiningsaid vapors with said oxygen not adsorbed by said adsorbent, a catalyst,comprising spongy platinum, means for applying said gases to saidplatinum, a photoelectric cell, means for applying radiations from saidplatinum to said cell, and means for indicating the magnitude of saidcurrent flowing in said cell. 1

9. In a radiant energy control device, a container containing gas, asource of radiant energy, means for varying th pressure of said gas insaid container, said last means comprising means for focusing saidradiant energy on said gas, ;a substance, means for producing a chemicalreaction between said substance and said gas, and means for indicatingthe amount of energy produced by said chemical reaction.

10. In a radiant energy control device, a source of gas, a container,means for passing a current of said gas through said container, meansfor varying the magnitude of the current of gas passing out of saidcontainer, said last means comprising means for impressing photons onsaid container, a substance, means for producing .-a chemical reactionbetween said current of gas passing out of said container and saidsubstance, and means for indicating the magnitude of energy released bysaid chemical reaction.

11. In a radiant energy control device, a container containing gas, anadsorbent, means for passing a current of said gas over said adsorbent,means for varying the magnitude of said current, said last meanscomprising means for impressing r radiant energy on said gas passingover said adsorbent, a second gas, means for producing a.

chemical reaction between said gas current and said second gas, andmeans for indicating the magnitude of energy released in said chemicalreaction.

12. The method of indicating the presence of radiations with a stream ofgas passing over an adsorbent which consists in, applying saidradiations to said adsorbent to produce compressional Waves in saidstream, in producing variations in light with said compressional wavesand in indicating said variations in said light.

13. A radiant energy receiving device comprising: an adsorbent, meansfor passing a stream 01' gas over said adsorbent, means for focusingphotons on said adsorbent to produce compressional waves in said stream,a source of light, a photo-electric cell, means for impressing lightquanta from said source on said cell, means for varying said lightquanta impressed on said cell with said compressional waves, and meansfor indicating the magnitude of said light quanta impressed on saidcell.

14. A radiant energy control device comprising: an adsorbent, means forpassing a stream of gas over said adsorbent, means for focusing photonson said adsorbent to produce variations in said stream, means forproducing variations in light with said variations in sa d stream, aphotoelectric cell, means for impressing said light variations on saidcell, and means for indicating said variations in light impressedon'said cell.

OLIVER T. FRANCIS.

